Wireless communication technologies, such as those used for NFC or ISO 14443 devices, communicate with each other via magnetic field induction in close distance. Each device features an antenna. The primary device (“reader” or “initiator”) generates the magnetic field which can be used to power secondary devices like passive transponders. Modulation schemes applied to the magnetic fields are used for communication purpose between the devices.
The primary device uses a transmitter to generate the emitted radio frequency (RF) field. A matching circuitry is used to transform and adapt the antenna impedance to the emitting device's transmitter.
Demand for high power emission can limit the NFC or RFID reader in high data rate communication. More specifically, as the coupling between the primary and secondary device increases, the overall Q (quality) factor of the two (or more) coupled circuits changes according to the coupling factor and the degree of detuning of the resonant circuit of the primary device. The resulting envelope of the transmitted signal is related to the resultant Q factor of the coupled systems.
Because the Q factor can vary greatly for such coupled systems, one single static configuration setting for the transmitter may not be sufficient to overcome this wide variation in Q factor and the resulting envelope shape of the transmitted signal. In compliance of the application system for transmitter signal shaping can occur depending on the distance/position of the secondary device with respect to the primary device. In particular, the transmitter envelope shape may be incompliant to standards.
Therefore, it is desirable to have devices and methods that can provide for dynamic transmitter signal envelope shaping control for NFC or RFID devices.